1. Field of the Invention
The present invention relates to a mold for resin-sealing of a semiconductor device.
2. Description of the Related Art
FIG. 4 is a cross-sectional view illustrating the lower mold half of a conventional resin-sealing apparatus disclosed in Japanese Published Patent Application 62-269328. A cavity 1b is formed in a molding board 1, and a cavity block 2 is incorporated into the cavity 1b. A plurality of cavities 2a are formed on the upper face of the cavity block 2, and a plurality of penetrating apertures 2c connecting the cavities 2a and the lower face of the cavity block 2 are formed. An ejecting pin 3 is inserted into each of the penetrating apertures 2c so as to freely travel, the lower end of each of the ejecting pins 3 being secured by means of a pressure plate 5 to the upper part of an ejector plate 4. The upper end of an ejecting rod 8 contacts the lower face of the ejector plate 4, and the ejecting rod 8 penetrates through the molding board 1 so as to extend downward. Further, a pot 7 for containing resin is formed in the central part of the cavity block 2, whereas the front end of a plunger 6 is inserted into the pot 7. Furthermore, heaters 1a and 2b are respectively buried in the molding board 1 and the cavity block 2.
An ejector block, composed of the cavity block 2, the ejecting pins 3, the ejector plate 4, and the pressure plate 5, is removably incorporated into the molding board 1 as an integral part, and is replaceable according to the kind of lead frames and semiconductor chips to be resin-sealed. FIG. 4 shows the lower mold half which is utilized together with an upper mold half having substantially the same structure as that of the lower mold half.
When resin-sealing is performed, a lead frame (not shown) is held on a parting plane 50 of the lower mold half so that a semiconductor chip (not shown) is contained in the cavity 2a, and at the same time resin (not shown) is introduced into the pot 7. Under these conditions, a press apparatus (not shown) clamps the lower mold half and the upper mold half (not shown). The resin in the pot 7 is then pressed by driving the plunger 6 upward and is introduced into the cavities 2a through a runner and gates formed in the upper mold half.
After the resin has set up, the upper mold half is separated from the lower mold half, and the ejector plate 4 is lifted upward by the ejecting rod 8. This causes the top end of each of the ejecting pins 3 to protrude into the inside of one of the cavities 2a, and the lead frames which have been resin-sealed are taken out of the cavities 2a.
Because of the structure through which the cavity block 2 is incorporated into the upper part of the cavity 1b that is formed in the molding board 1, the stiffness of the molding board 1 at the periphery of the parting plane 50 greatly differs from that of the cavity block 2 at the center of the parting plane 50. For this reason, when a clamping force acts on the lead frame as a result of clamping the upper and lower mold halves, the parting plane 50 is deformed, as illustrated in FIG. 5, and it is therefore impossible to press the lead frame evenly. Consequently, this leads to a problem in that flashing is formed on the surface of the lead frame in accordance with the amount B of deformation of the parting plane 50.